Been there and took too fucking long to done that

Now it's 3 times they cancel/ stand up/ turn down and I don't bother again

In our situation it was after the second refusal to meet.

I think this is a huge problem with the online world. We suffer social anomie as we lack an established set of norms and values for engaging with people online.
Are the people we see in the profile really who they say they are? I suspect that you and me are who we are in real life. There are others who hide behind cartoons and we can see that. But there are those who fall into the category of 'Catfish'. Sometimes they fun to deal with, but others are a pain in the arse.
For me, I get concerned that I'll be mistaken for some creepy stalker if I keep communicating for a few emails past them going quiet. So I set my own rule of three. They may be away and can't email. I work most weekends with no internet access and long hours, often 32 hour shifts.
It is a hard call to make.

Just cutting off communication without explanation is a pretty crappy way to behave. I ask for an explanation, and if none is forthcoming or satisfactory, then I flush them out.

In this parallel universe or in real life?

I don't. People got their own shit to be going on with. Sometimes your lives just don't line up, they might later. People fall in and out of communication all of the time. Now... If they are making plans and flaking, that's another thing. But, even then, I just stop making plans. It takes a real breach to get me to write a friend off.

Why cut them off all together? Do other things and revisit the situation at a later day or dont. I think It's nice to have people out there even if I don't carry on an active relationship day to day due to life.

Most of my friends live in different countries if not different states. The ones left in my state have kids, grandkids, jobs, obligations. Unless someone tells me to go to hell in a hand basket, they're still my friend.